The present invention generally relates to printing technology, and more particularly to coupling a barrier layer to a substrate of a fluid ejection device.
Substantial developments have been made in the field of electronic printing technology. A wide variety of highly-efficient printing systems currently exist which are capable of dispensing ink in a rapid and accurate manner, including thermal inkjet systems. The ink delivery systems described herein (and other printing units using different ink ejection devices) typically include an ink containment unit (e.g. a housing, vessel, or tank) having a self-contained supply of ink therein in order to form an ink cartridge. In a standard ink cartridge, the ink containment unit is coupling with the remaining components of the cartridge to produce an integral and unitary structure wherein the ink supply is considered to be xe2x80x9con-board.xe2x80x9d
Printing units using thermal inkjet technology basically involve an apparatus which includes at least one ink reservoir chamber in fluid communication with a substrate (preferably made of silicon and/or other comparable materials) having a plurality of thin-film heating resistors thereon. The substrate and resistors are maintained within a structure that is characterized as a xe2x80x9cprinthead.xe2x80x9d Selective activation of the resistors causes thermal excitation of the ink materials stored inside the reservoir chamber and expulsion thereof from the printhead. Representative thermal inkjet systems are discussed in U.S. Pat. Nos. 4,500,895 to Buck et al.; 4,794,409 to Cowger et al.; 4,509,062 to Low et al.; 4,929,969 to Morris; 4,771,295 to Baker et al.; 5,278,584 to Keefe et al.; and the Hewlett-Packard Journal, Vol. 39, No. 4 (August 1988), all of which are incorporated herein by reference.
A typical printhead will have at least one or more ink ejectors (e.g. thin-film resistor elements in a thermal inkjet system) on a substrate. The ink ejectors are each positioned within a compartment defined as a xe2x80x9cfiring chamberxe2x80x9d. Ink materials are then delivered to the firing chambers and thereafter expelled on-demand by the ink ejectors. Between and around the firing chambers on the substrate are numerous conductive circuit elements which electrically communicate with the ink ejectors and other components on the substrate. The circuit elements also communicate with the operating components of the printer unit that generate the electrical signals.
Positioned directly over the circuit elements and exposed portions of the underlying substrate is a composition defined as an xe2x80x9cink barrier materialxe2x80x9d or xe2x80x9cink barrier layerxe2x80x9d or xe2x80x9cchamber layerxe2x80x9d. The ink barrier material functions as an electrical insulator and xe2x80x9csealantxe2x80x9d which covers these components and prevents them from coming in contact with the ink compositions being delivered. Likewise, the ink barrier material protects the circuit elements from physical impact, contaminants, and the like. As a result, electrical shorts, breaks, and similar problems are avoided which improves the overall reliability and longevity of the printing system under consideration.
Many different chemical compositions may be used to fabricate the ink barrier layer, with organic compositions (e.g. polymers and other related materials), including those with a high dielectric constant. After placement of the ink barrier material (preferably in a discrete layer) on the underlying substrate and thin-film circuitry, an orifice plate with multiple ink ejection openings therethrough is positioned on the barrier layer and over the firing chambers which contain the ink ejectors. The orifice plate is then adhesively or otherwise affixed in position.
A factor in printhead design involves the overall structural integrity of the entire printhead unit. The term xe2x80x9cstructural integrityxe2x80x9d as used herein generally concerns the ability of the individual components in the printhead to remain affixed together in a strong and cohesive manner without the detachment or delamination of any elements. It is desired that ink xe2x80x9cbarrierxe2x80x9d materials within the printhead are securely attached to the underlying thin film circuitry and substrate associated therewith.
Notwithstanding the beneficial features discussed above, problems may arise in printhead systems if the barrier layer xe2x80x9cdelaminatesxe2x80x9d or otherwise detaches in a complete or partial manner from the underlying substrate and circuitry thereon. These problems typically cause (1) ink xe2x80x9cshortsxe2x80x9d in which ink from the firing chambers and adjacent regions in the printhead xe2x80x9cwicksxe2x80x9d into any gaps formed between the thin-film circuitry and the barrier layer; (2) undesired changes in firing chamber architecture caused by barrier delamination around the chambers; and/or (3) the propagation of additional cracks, fissures, gaps, stress lines, and the like once the initial delamination of the barrier layer occurs. All of these undesired situations can lead to improper ink drop ejection, decreased longevity, reduced reliability, and an overall deterioration in print quality. Accordingly, gap-free adhesion of the substrate (and circuitry thereon) to the ink barrier layer is desired.
The chemical interactions which adhere these components to each other within the printhead are not well understood from a molecular standpoint. However, it is currently believed that the chemical bond between the organic ink barrier layer and the substrate having the electrical circuitry thereon is one of the weakest and most potentially troublesome in the entire printhead structure. In attempting to solve this problem, the following diverse approaches have been considered: (1) elaborate cleaning and xe2x80x9cdecontaminationxe2x80x9d of the substrate, thin-film electrical circuitry, and surrounding components; (2) chemical modification of the barrier layer, substrate, and/or electrical circuit elements; and/or (3) the use of additional (e.g. supplemental) chemical adhesive materials. However, it is not currently believed that any of these approaches provide sufficient results from a cost, efficiency, and structural design standpoint. Thus, there is a desire for an effective solution to the foregoing problem in which a high degree of structural integrity is maintained between the ink barrier layer and substrate/thin-film circuitry in an inkjet or other ink delivery printhead.
Therefore, it is desirable to (1) prevent delamination problems between the ink barrier layer and underlying thin-film structures in a wide variety of different thermal inkjet and non-thermal-inkjet printheads; (2) avoid electrical shorts and undesired changes in printhead architecture which may occur when barrier layer delamination takes place; (3) improve adhesion between the ink barrier layer and the circuit-containing substrate without using supplemental adhesives and elaborate decontamination procedures; (4) avoid crack propagation throughout the printhead which can result from ink barrier layer delamination; and (5) accomplish these goals in an economical manner which is especially well-suited for use on a mass production scale.
One embodiment of a method of coupling a barrier layer to a substrate of a fluid ejection device includes disposing a mechanical intercoupling structure on a substrate at least one fluid ejector thereon; disposing a chamber layer over said substrate, wherein side walls of an ejection chamber are defined by the chamber layer; and substantially embedding said mechanical intercoupling structure with the chamber layer.